JPH04267223A - Ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To obtain a ferroelectric liquid crystal element having a large capacity and a high contrast by interposing ferroelectric liquid crystal formed of a specific compound between substrates, and by specifying the structure thereof. CONSTITUTION:Each of a pair of insulation substrates is formed thereon with an electrode, an insulating film and an orientating film. Rubbing and orientation are carried out in the same direction for the pair of insulation substrates, liquid crystal moleculars having a pretilt angle of greater than 8 deg. at the interface between the liquid crystal and the orientating film. The liquid crystal phase to be driven is a killer smetic C-phase in which a smetic layer has a chevron structure in which the layer bends, and the direction of the rubbing and orientation process is reverse to the layer bending direction in a drive temperature range. Further, the orientating condition of the ferroelectric liquid crystal is uniform and is made of more than 95wt.% of a compound given by a formula.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal display element. More specifically, the present invention relates to a matrix-type large-capacity ferroelectric liquid crystal element with high contrast and a method for driving the same.

0002

[Prior Art] Currently, liquid crystal display elements are used in a wide range of fields such as watches, calculators, office automation equipment such as word processors and personal computers, and pocket televisions. This is what was used.

[0003] As a liquid crystal display device using nematic liquid crystal, twisted nematic type (Twisted nematic type) is used.
Nematic TN type) liquid crystal display device, Supertwisted type (Supertwisted Bire)
frequency effect, SBE type) liquid crystal display devices.

However, twisted nematic liquid crystal display elements have the drawback that as the number of scanning lines increases, the drive margin becomes narrower and sufficient contrast cannot be obtained, making it difficult to produce large-capacity display elements. be. Super twisted nematic (STN) type liquid crystal display elements and double layer super twisted nematic (DSTN) type liquid crystal display elements have been developed to improve this TN type liquid crystal display element, but as the number of lines increases, contrast and response speed deteriorate. As a result, the display capacity is currently limited to about 800×1024 lines.

On the other hand, thin film transistors (TFTs) are formed on the substrate.
) has also been developed, making it possible to display large-capacity displays such as 1,000 x 1,000 lines, but the manufacturing process is long, yields are likely to drop, and manufacturing costs are extremely high. It has the following drawbacks. Furthermore, this method is considered difficult to fabricate a large capacity display element such as 2000×2000 lines due to restrictions due to the mobility of the semiconductor.

[0006] However, the demand for display devices in the world is moving toward higher resolution.
In particular, DTP (Desk Top Publishing)
ng), EWS (Engineering Work
WYSIWIG (W
what you see is what you see
The concept of ``et'' is being emphasized. this is,
The concept is to display the same thing as what is printed out on the display device. The resolution of current laser printers is about 400 DPI (400 dots/inch), so in order to realize the WYSIWYG concept, a display device that is at least A4 size or larger and has a resolution of 2000 x 2000 or more is required.

As mentioned earlier, it is difficult to achieve a resolution of 2000 x 2000 or more with conventional liquid crystal display devices using a nematic phase; Ferroelectric liquid crystal display elements (Appl. Phys. Lett., 36,
899 (1980); JP-A-56-107216; US Pat. No. 4,367,924). This liquid crystal display element differs from the above-mentioned field effect type nematic liquid crystal display device that utilizes the dielectric anisotropy of liquid crystal molecules. It is a switching liquid crystal display element.

This display method uses chiral smectic C phase, chiral smectic I phase, and chiral smectic F phase.
This method utilizes a ferroelectric liquid crystal phase such as a ferroelectric liquid crystal phase. In this ferroelectric liquid crystal device, when ferroelectric liquid crystal is injected into a cell with a thin cell gap, the helical structure of the ferroelectric liquid crystal unravels under the influence of the interface, and the liquid crystal molecules are tilted at an angle θ with respect to the normal to the smectic layer. There is a coexistence of a region that is stable when tilted by -θ and a region that is stable when tilted by -θ in the opposite direction, and has bistability. When a voltage is applied to this ferroelectric liquid crystal element, the orientation of the liquid crystal molecules and their spontaneous polarization can be uniformly aligned, and by switching the polarity of the applied voltage, the orientation of the liquid crystal molecules can be changed from one certain state to another. Switching to a certain state becomes possible. With this switching, birefringent light changes in the ferroelectric liquid crystal in the cell, so by sandwiching the ferroelectric liquid crystal element between two polarizers, transmitted light can be controlled. Furthermore, even if the voltage application is stopped, the orientation of the liquid crystal molecules is maintained in the state before the voltage application was stopped due to the alignment regulating force of the interface, so that a memory effect can also be obtained. In addition, the time required for switching drive is 1/1000 or less of that of a twisted nematic liquid crystal display device, which enables high-speed response because the spontaneous polarization of the liquid crystal and the electric field act directly.

As described above, the characteristics of this ferroelectric liquid crystal element include bistability, memory performance, and high-speed response. Therefore, using this ferroelectric liquid crystal, it is possible to construct a high-resolution liquid crystal display device with a large number of scanning lines using a multiplex drive method, and since it does not require active elements such as thin film transistors, manufacturing is possible. It has the advantage that the cost does not increase. In addition, ferroelectric liquid crystal elements also have the advantage of wide viewing angles, making WYSIWIG (What you
see is what you get. ) is seen as a highly promising device for large-capacity display.

0010

[Problems to be Solved by the Invention] Ferroelectric liquid crystal elements have the above-mentioned advantages, but it is difficult to achieve flicker-free, high-contrast display in large-capacity display elements having 1000 x 1000 or more scanning lines. If you try to do so, the following problems will arise.

[0011] That is, one method for achieving flicker-free display is to
In this case, the ferroelectric liquid crystal material is required to have an extremely fast response speed. for example,
In the case of a display element with 1000 scanning lines, a high-speed response of 8.4 μsec is required, as can be seen from the following equation.

[0012] 16.7 (msec) ÷ 1000 ÷ 2 = 8
．． 4 μsec (Here, it is divided by 2 because in the case of ferroelectric liquid crystal, at least 2 pulses are required for writing.)

[0013] For this reason, in the research and development of ferroelectric liquid crystal materials to date, the realization of high-speed response has been a major goal. Previous research has shown that in order to improve response speed, it is possible to create a ferroelectric liquid crystal composition by adding a chiral compound with large spontaneous polarization to a low-viscosity non-chiral liquid crystal composition that exhibits a smectic C phase. I've found it to be good. For this reason, many efforts have been made to develop optically active compounds with extremely large spontaneous polarization (for example, at the 16th Liquid Crystal Symposium,
1K101, 1K102, 1K111, 1K11
2, 1K114, 1K115, 1K116, 1
K117, 1K119, 3K106, (1990
), ), On the other hand, also in non-chiral liquid crystal compositions, there is knowledge that pyrimidine compounds are preferable due to their low viscosity (for example; Onishi et al., National Technica
l Report, 33, 35 (1987). ) was obtained.

However, it is currently not easy to achieve the required response speed by improving ferroelectric liquid crystal materials. Furthermore, if we take into account that in order to create a display element with a larger capacity, the response speed must be further increased, it becomes quite difficult to increase the capacity by increasing the speed of the liquid crystal material. It's easy to imagine.

[0015] As a powerful method for solving such problems, a method called partial rewriting (Kanbe, Institute of Electronics, Information and Communication Engineers Special Seminar Proceedings "Optoelectronics" - Liquid Crystal Displays and Related Materials -, 1990) January,
p18-26) are proposed. This method accesses only the parts of the screen that need to be rewritten. This enables a display element that can follow movements of a mouse, etc., which require high speed when displaying graphics.

However, when attempting to obtain a flicker-free display using this partial rewriting method, a bias voltage of 1/3 of the writing voltage is applied to pixels that are not to be rewritten (hereinafter, this driving method will be described). (referred to as 1/3 bias drive method).

FIG. 1 shows an example of the 1/3 bias driving method proposed in Japanese Patent Laid-Open No. 64-59389. That is, as shown in FIG. 2, a ferroelectric liquid crystal is interposed between a plurality of scanning electrodes L and a plurality of signal electrodes S arranged in directions that intersect with each other. A ferroelectric liquid crystal is used as a pixel, a signal voltage with a waveform corresponding to display data is applied to the signal electrode S, and a selection voltage with a waveform that can rewrite the display state of the pixel on the electrode is applied to the scanning electrode L. In the sequential application driving method, the waveform shown in FIG. 1 (1) is applied to the scanning electrode L, and a selection voltage A is applied to the scanning electrode L to rewrite the memory state of the pixel on the scanning electrode L, that is, the displayed brightness state. The waveform shown in FIG. 1 (2) is applied to the scanning electrode L, but it is a non-selection voltage that cannot rewrite the memory state of the pixel on the scanning electrode L, that is, the displayed brightness state. This is the waveform of B. The waveform shown in FIG. 1 (3) is the waveform of the rewrite bright voltage C applied to the signal electrode S when rewriting the pixel to the "bright" luminance state, and the waveform shown in FIG. '' is the waveform of the rewrite dark voltage D applied to the signal electrode S when rewriting to the brightness state of
The waveform shown in FIG. 1(5) is the waveform of the non-rewriting voltage G applied to the signal electrode S when the display state of the pixel is not rewritten. 1 (6) to (11) show the waveforms of the voltage applied to the pixel Pij, among which waveforms A to C in FIG. Figure 1 shows the waveform when voltage C is applied.
Waveforms A-D in (7) show the waveforms when selection voltage A is applied to the scanning electrode Li and rewriting dark voltage D is applied to the signal electrode Sj, and waveforms A-G in FIG. Electrode L
The waveforms shown are when the selection voltage A is applied to the signal electrode Sj and the non-rewriting voltage G is applied to the signal electrode Sj, and the waveform B-C in FIG. The waveform B-D in FIG. 1 (10) shows the waveform when the rewriting bright voltage C is applied to the signal electrode Sj, and the waveform B-D in FIG. Waveforms BG in FIG. 1 (10) show waveforms when non-selection voltage B is applied to scan electrode Li and non-rewriting voltage G is applied to signal electrode Sj. Therefore, the voltage waveform shown in Figure 1 (6) is applied to the pixel whose display content is rewritten from "dark" to "bright", and the voltage waveform shown in Figure 1 (6) is applied to the pixel whose display content is rewritten from "bright" to "dark". 7
) is applied to the pixel, and any voltage waveform of FIG. 1 (8), (9), (10), or (11) is applied to the other pixels. Well, here,
In the waveforms of Figures 1 (6) and (7), 3VD or -3
Although the VD voltage is applied, (8), (9), (10), (
11), a voltage of 1/3 VD or -VD is applied. By using such waveforms, waveforms (8), (9), (10), when display contents are not rewritten,
(11) It is possible to eliminate the voltage peak value difference, and a flicker-free display can be obtained.

Now, the biggest problem when using this 1/3 bias method is that the 1/3 bias method is applied even to pixels that are not rewritten.
A bias voltage of 3 is applied, and this bias voltage causes fluctuations in the molecules of pixels that are not rewritten, resulting in a decrease in contrast. For example, a ferroelectric liquid crystal display prototyped by Canon using the partial rewriting method achieved a contrast of only 5:1 (Kanbe, Institute of Electronics, Information and Communication Engineers Special Seminar Proceedings ``Optoelectronics'' - Liquid Crystal Display and related materials
, January 1990, p18-26). In addition, we have previously created display devices by combining various ferroelectric liquid crystal compositions with liquid crystal elements of various configurations, but the contrast obtained when displaying using the 1/3 bias driving method The value was about 1.5 to 8, and the product was extremely unsatisfactory.

On the other hand, research has been actively conducted to improve contrast. For example, there is research using the SiO oblique evaporation method. This method uses oblique deposition to impart a relatively high pretilt to the substrate interface, thereby preventing layer bending and achieving an obliquely inclined layer structure (Kamimura, et al., National Tec
hnical Report, 33(1), 51
(1987). ). A method has also been reported in which the layer structure is changed to a bookshelf structure by applying a high voltage alternating electric field to a liquid crystal cell having a chevron structure. (Sato et al., 12th LCD Symposium, 1F16 (198
6). ). These reports all state that high contrast characteristics were obtained. However, the above-mentioned oblique evaporation method has major problems in terms of production, such as the difficulty in achieving a uniform evaporation angle within the substrate and the need for a vacuum process, which increases the cost of the manufacturing equipment. In addition, with the method of applying an electric field described below, it is difficult to uniformly change the layer structure within the liquid crystal cell, and in many cases the structure gradually changes to the original chevron structure over a long period of time, so it has not yet been put to practical use. not present. In addition, the above-mentioned 1/
There have been no reports of driving these elements using the three-bias driving method, and at this stage it is highly questionable whether a large-capacity, high-contrast display element can be realized by such a method.

[0020]

[Means and effects for solving the problem] The researchers of the present invention have conducted extensive research with the aim of obtaining good contrast in the 1/3 bias driving method and satisfying other specifications necessary for practical use. As a result, the present invention was achieved.

That is, in the present invention, a pair of substrates are formed by selectively forming electrodes on their surfaces, then forming an insulating film and an alignment film, and then subjecting the alignment film to a rubbing alignment treatment.
In a ferroelectric liquid crystal display element, a pair of ferroelectric liquid crystals are arranged to face each other, a ferroelectric liquid crystal is interposed between the substrates, and the ferroelectric liquid crystal is driven by selectively applying a voltage to the electrodes. The direction of the rubbing alignment treatment of the substrate is parallel, the liquid crystal phase to be driven is a chiral smectic C phase, and the smectic layer structure in the chiral smectic C phase has a chevron structure bent in a dogleg shape, The direction of the rubbing alignment treatment and the bending direction of the layer are opposite to each other, the pretilt angle of the liquid crystal at the interface with the alignment film is 8° or more, and the alignment state of the ferroelectric liquid crystal is uniform. There is provided a ferroelectric liquid crystal element, characterized in that the ferroelectric liquid crystal contains 95% by weight or more of the compound of general formula (I).

Of course, the driving method of the element of the present invention is 1/3
Needless to say, the present invention is not limited to the bias driving method, and other driving methods are applicable.

Next, the present invention will be explained in detail. FIG. 3 is a cross-sectional view showing an example of the liquid crystal element of the present invention. Glass substrate 1
A plurality of transparent electrodes 2a are arranged in stripes parallel to each other, and an insulating film 3a is formed on the transparent electrodes 2a.
, an alignment film 4a is formed, and a uniaxial alignment process is performed on the alignment film 4a by rubbing to form a substrate 9. On the other hand, on the other side of the glass substrate 1b, a plurality of transparent electrodes 2b are formed in a stripe pattern parallel to each other under the same conditions, and an insulating film 3b and an alignment film 4b are formed thereon. Then, the alignment film 4b is subjected to a rubbing alignment treatment to form the substrate 10.

Next, this substrate 10 and the other substrate 9 are arranged so that the alignment films 4a and 4b face each other, the transparent electrodes 2a and 2b are perpendicular to each other, and the rubbing directions are almost the same. They are pasted together with a sealing member 6 with an interval of about 3 μm between them. A liquid crystal cell 11 is created by interposing a ferroelectric liquid crystal 7 between these substrates 9 and 10. Furthermore, a polarizing plate 12 whose polarization axis is substantially perpendicular to the top and bottom of this cell is provided.
a and 12b, and the polarization axis of one of the polarizing plates is substantially aligned with the optical axis of either one of the liquid crystals of the cell, thereby forming a liquid crystal display device.

Now, it is known that in such a ferroelectric liquid crystal element, the layer structure of the chiral smectic C layer generally has a chevron structure that is twisted into a dogleg. There is. By the way, as shown in FIG. 4(a), there are two directions (17, 18) in which this layer bends, and two different orientation states occur accordingly. At this time, an alignment defect called a zigzag defect occurs where the direction of bending of the layer changes. Figure 4(b) is a schematic diagram of a zigzag defect observed using a polarizing microscope. Zigzag defects can be classified into defects called lightning defects (15) and defects called paired pin defects (16). can. As a result of previous research, it has been found that parts with a layer structure of <<>> correspond to lightning defects, and parts with a layer structure of >><< correspond to hairpin defects. It has become clear (Jpn. J. Appl. Phys.
, 28, 50 (1988). ).

Now, these two orientations are called the C1 orientation and the C2 orientation due to their relationship with the rubbing direction (Kanbe, Institute of Electronics, Information and Communication Engineers Special Seminar Proceedings ``Optoelectronics'' - Related to Liquid Crystal Displays) Materials, January 1990, p18-26). FIG. 5 is a diagram for explaining these two orientations. The conical shape shown in Figure 5 is a trajectory in which liquid crystal molecules can move during switching.
The trajectory is inclined by the tilt angle 26 of the liquid crystal with respect to the layer normal 25. Regarding this relationship, please refer to Japanese Patent Application Laid-open No. 1-1584.
15, and the case of 23 where the rubbing axis and the bending direction of the layer are the same is called C1 orientation (chevron 1
), and the opposite case of 24 is defined as C2 orientation (chevron 2). The C1 orientation and the C2 orientation show almost equivalent alignment states when there is no pretilt of the liquid crystal molecules at the substrate interface, but when uniaxial alignment treatment such as rubbing treatment is applied, the liquid crystal molecules change in the direction shown in Figure 6. Pre-tilt 2
2 occurs. When this pretilt is increased, the difference in the orientation state of liquid crystal molecules between the C1 orientation and the C2 orientation becomes remarkable. The researchers of the present invention have confirmed that the difference is significant if the pretilt angle is about 2° or more. Also,
It has also been reported that the C1 orientation tends to appear at higher temperatures (Kanbe, Institute of Electronics, Information and Communication Engineers Specialized Seminar Proceedings "Optoelectronics" - Liquid Crystal Displays and Related Materials -, January 1990, p-18-26.).

FIG. 7 shows a schematic diagram showing switching of a ferroelectric liquid crystal. Switching between a⇔b and between c⇔d is a schematic representation of the state of molecules (C director) in the memory state of C1 orientation and C2 orientation when molecules are difficult to move in the substrate field. In this case, the memory state switching occurs only around the connecting portion 14 of the chevron structure. In other words,
It can be said that molecules are not switching at the substrate interface, and this memory state is usually called twisted orientation. In this case, considering the arrangement of molecules at the interface, the n-director 20 is in a largely twisted state in the C1 orientation, and conversely in a small twisted state in the C2 orientation. Therefore, it is expected that the C1 orientation is easier to obtain a twisted orientation. In fact, JP-A-1584
According to No. 15, when polarizing plates are arranged perpendicularly above and below a cell and the cell is rotated therein, there is no place where the light is quenched in the C1 orientation, and there is a place where the light is quenched in the C2 orientation.
It has been reported that better contrast characteristics can be obtained with the C2 orientation than with the C1 orientation.

Such results are often obtained when the pretilt angle of the alignment film is small, and similar results were confirmed by the researchers of the present invention. We found that a different phenomenon occurs when the angle is larger. That is, when using an alignment film with a large pretilt angle of 8° or more, in the C1 orientation on the high temperature side, a region showing a clear extinction position and a region showing no extinction position are observed, and in the C2 orientation on the low temperature side, a region showing a clear extinction position and a region showing no extinction position are observed. In the orientation, only regions exhibiting clear extinction positions are observed. It is generally accepted that uniform orientation and twisted orientation can be distinguished by the presence or absence of an extinction position (Fukuda, Takezoe, "Structure and physical properties of ferroelectric liquid crystals",
Coronasha, 1990, p-327), here and now, C
1 orientation that exhibits an extinction position is C1U (C1 uniform) orientation, and C1 orientation that does not exhibit an extinction position is C1T (C1 orientation).
1 twist) orientation. As for C2 orientation, only one type of orientation was obtained, so it will be referred to only as C2 orientation.

If we consider this phenomenon a little more, we can say the following. In other words, the phenomenon explained using a￣d in FIG. 7 was described for the case where molecules are difficult to move at the substrate interface, but by making the molecules near the interface easier to move,
The situation becomes different when considering the case where interface inversion occurs. Figure 7e, f, g, h are C when interface inversion occurs.
This figure shows the appearance of molecules in memory states in 1 orientation and C2 orientation. Switching when an electric field is applied is e
Occurs between ⇔f and between g⇔h. In this case, in the C1 orientation, the twisted state of the molecules of the upper and lower substrates disappears in both the two memory states, and the optical axis angle (memory angle) between the two memory states becomes wider. Therefore, not only is quenching possible in crossed Nicols, but the cell can also be placed in the quenching position.
When voltage is applied and the optical axis is switched to another memory state, the movement of the optical axis angle is large, resulting in a large optical change. On the other hand, in the C2 orientation, even if molecules near the interface are inverted, as can be seen from the figure,
First memory state (g) and second memory state (h)
The change in the optical axis between the two is small. Therefore, it can be estimated that higher contrast can be obtained with the C1 orientation. We understand that when a high pretilt alignment film is used, molecules generally move more easily at the substrate interface, and we believe that this is linked to the above phenomenon.

Now, when an alignment film with a large pretilt angle is used, three alignment states, C1U, C1T, and C2, are observed, but the partial rewriting method was performed using 1/3 bias drive. The researchers of the present invention have found that the contrast obtained has the following tendency when C1U>C2>C1T

[0031] That is, conventional knowledge (for example, Kannabe, Institute of Electronics, Information and Communication Engineers Specialized Seminar Proceedings "Optoelectronics" - Liquid Crystal Displays and Related Materials -, January 1990,
p18-26. ), it has been said that better contrast can be obtained by using the C2 orientation, which appears at lower temperatures, and therefore it is preferable for the transition from C1 orientation to C2 orientation to occur at as high a temperature as possible (this (It is necessary to confirm that even if the pretilt of the liquid crystal at the interface between the alignment film and the liquid crystal is high, found that high contrast could be obtained by performing 1/3 bias driving using C1U orientation.

[0032] When the pretilt is high, the C1U orientation is reduced to 1/
The reason why high contrast is obtained when driving with 3 bias driving is not completely clear, but at least the present inventors have found that the fluctuation of molecules when a bias voltage is applied is smaller than in the C2 orientation. It has been confirmed that light transmission in the black state is small.

Now, how to distinguish between the orientations of C1U, C1T, and C2 will be described. First, how to distinguish between C1 orientation and C2 orientation, the bending direction of the layer can be determined from the shape of zigzag defects occurring within the cell. There are two types of defects: lightning and hairpin, and by observing the directions of these two defects, the relationship between the rubbing direction and the bending direction of the layer can be determined (see Figure 4). On the other hand, since it is generally accepted that the relationship between the rubbing direction and the pretilt direction of the molecule is as shown in FIG. 6, the C1 orientation and the C2 orientation can be distinguished using these relationships.

Next, how to determine whether the orientation is twisted (T) or uniform (U), in this patent, of the two states, the state in which the extinction position appears is defined as uniform, and the state in which it does not appear is defined as twisted. I mentioned that earlier.

Furthermore, uniforms and twists can be distinguished by observing inverted domains. That is,
When observing a ferroelectric liquid crystal cell under a microscope while applying a low-frequency triangular wave, an inverted domain is observed. On this occasion,
Domain inversion (called a boat-shaped domain) due to movement of internal dislocations that occurs at chevron connections occurs regardless of whether the orientation is twisted or uniform. Therefore, if one or more domain inversions are observed in addition to this inversion, it can be determined that the inversion is at the interface, and that the orientation is uniform.

Now, as described above, in the present invention, by using the C1U orientation created using an alignment film with a large pretilt angle, a partial rewriting method is performed using 1/3 bias drive. They found that good contrast could be obtained when
Unfortunately, bistable switching of the C1U orientation cannot be achieved using any ferroelectric liquid crystal material. If an inappropriate material is used, the C2 orientation may occur in the driving temperature range, or the C1T orientation may occur even if the C1 orientation is achieved.
Or, even if CIU orientation can be achieved, switching may not occur, or the temperature range thereof may be extremely narrow. In fact, the present inventors have applied ferroelectric liquid crystals that have been created so far and commercially available or sample-provided ferroelectric liquid crystals to the above-mentioned ferroelectric liquid crystal elements; At CIU
Orientation switching could not be realized.

The ferroelectric liquid crystal material is also required to have high-speed response, good orientation, good chemical stability, good optical stability, and appropriate refractive index anisotropy. As a result of extensive research into ferroelectric liquid crystal materials that meet these conditions, the present researchers combined a liquid crystal composition containing 95% by weight or more of the compound of general formula (I) below with the above-mentioned liquid crystal element. The inventors have discovered that, by doing so, it is possible to produce a liquid crystal element that exhibits C1U orientation over a wide temperature range centered around room temperature and exhibits good contrast under 1/3 bias driving.

[0038]

[C7]

The present inventors have also found that it is preferable that the tilt angle of the liquid crystal is not 5° greater than the pretilt angle of the liquid crystal at the interface between the liquid crystal and the alignment film.

Examples of compounds belonging to the general formula ( ) include compounds of the sub-formulas (II) to (VI).

[0041]

[Chemical formula 8]

[0042]

[Chemical formula 9]

[0043]

[Chemical formula 10]

[0044]

[Chemical formula 11]

[0045]

[Chemical formula 12]

Straight-chain or branched alkyl groups in the definitions of formulas (I) to (VI) include methyl, ethyl, propyl, i-propyl, butyl, i-butyl, pentyl, 1
- or 2-methylbutyl, hexyl, 1- or 3-methylpentyl, heptyl, 1- or 4-methylhexyl,
Octyl, 1-methylheptyl, nonyl, 1- or 6-
Includes methyloctyl, decyl, 1-methylnonyl, undecyl, 1-methyldecyl, dodecyl, 1-methylundecyl, and the like. Further, the linear or branched alkyloxy group in the definitions of formulas (I) to (V) includes those in which an ether group is bonded to the above alkyl group. The carbon chain of these alkyl groups or alkyloxy groups may contain an asymmetric carbon. In addition, one or more hydrogen atoms in these alkyl groups or alkyloxy groups may be a fluorine atom, a chlorine atom, a bromine atom, a cyano group, a nitro group,
It may be substituted with a trifluoromethyl group, a methoxy group, etc.

Examples of compounds represented by sub-formula (II) include:

[Chemical formula 13] Examples include.

Examples of compounds represented by sub-formula (IV) include:

[Chemical formula 14] etc.

Examples of compounds represented by sub-formula (III) include:

[Chemical formula 15] etc. can be given.

Examples of compounds represented by sub-formula (V) include:

[Chemical formula 16] etc. can be given.

Examples of compounds represented by sub-formula (VI) include:

[Chemical formula 17] etc. can be given.

[0052]

[Example] Example 1 Compound No. shown in Table 1. Liquid crystal composition No. 101 to 112 having the composition shown in Table 2 was prepared. 201 to 203 were produced. These liquid crystal compositions exhibited a smectic C phase at room temperature. Table 3 shows the phase transition temperatures of these compositions.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

Example 2 An ITO film with a thickness of 1000 Å was formed on each of two glass substrates, a SiO2 insulating film with a thickness of 500 Å was formed on it, and the alignment film shown in Table 4 was coated on this using a spin coater. Te4
The film was formed to a thickness of 0.00 Å, and then uniaxially aligned by rubbing with a rayon cloth. A liquid crystal cell was fabricated by bonding these substrates to a thickness of 20 μm so that the rubbing directions were antiparallel. Nematic liquid crystal E-8 manufactured by Merck was injected into this, and the pretilt angle of the liquid crystal molecules from the substrate was measured using a magnetic field capacitance method. Table 4 shows the results.
Shown below.

[0057]

[Table 4] Example 3 A ferroelectric liquid crystal element having the configuration shown in FIG. 3 was manufactured. A plurality of ITO transparent electrodes 2a with a thickness of 1000 Å are arranged in stripes in parallel with each other on a glass substrate 1a, and an insulating film 3a of 500 Å of SiO2 is formed on the glass substrate 1a.
2 is formed, and then PSI-X-A- is formed as an alignment film 4a.
2001 (polyimide manufactured by Chisso Petrochemical Co., Ltd.) was formed to a thickness of 400 Å using a spin coater, and then uniaxially aligned by rubbing with a rayon cloth to form a substrate 9. On the other hand, the other glass substrate 1b was also processed under the same conditions to form the substrate 10.

Next, this substrate 9 and the other substrate 10
are made of epoxy resin with an interval of 1.5 μm interposed between them so that the alignment films 4a and 4b face each other, the transparent electrodes 2a and 2b are orthogonal to each other, and the rubbing directions are almost the same. They were bonded together using a sealing member 6. Between these substrates 9 and 10, ferroelectric liquid crystal composition No. 1 prepared in Example 1 was inserted through the injection port using a vacuum injection method. 201
203 were respectively injected, and the injection ports were cured with an acrylic UV-curable resin to create a liquid crystal cell 11. Furthermore, polarizing plates 12a and 12b with polarizing axes substantially perpendicular to each other are placed above and below this cell, and one polarizing axis of the polarizing plate is made to substantially match the optical axis of either one of the liquid crystals in the cell, thereby creating a liquid crystal display device. did.

When we investigated the orientation of these ferroelectric liquid crystal elements, we found that in the temperature range from the smectic C-smectic A transition point to room temperature, a small C2 orientation surrounded by minute zigzag defects was observed. Except for the area,
The entire surface had C1U orientation.

The tilt angle θ and memory angle θM in the chiral smectic C phase of these ferroelectric liquid crystal elements were measured. The tilt angle θ was defined as 1/2 of the angle between two extinction positions obtained by applying a ±10 V rectangular wave to the liquid crystal cell. The memory angle θM was defined as 1/2 of the angle between the two memory states obtained by applying a voltage having the waveform shown in FIG. 8(a). θ, θM, and θM/θ were plotted against temperature (FIGS. 9 to 11).

The voltage of the waveform shown in FIG. 8(a) (V=±20
V) was applied and the memory pulse width was measured. The memory pulse width was set to the minimum pulse width that allowed bistable switching. Set the pulse width to the memory pulse width,
When the waveform shown in FIG. 8(a) was applied, a contrast of 30 or more was obtained.

A voltage (V=±20 V) with a 1/3 bias waveform shown in FIG. 8(b) was applied, and the memory pulse width was measured. The memory pulse width was set to the minimum pulse width that allowed bistable switching. The results are shown in FIGS. 9 to 11. Also, by setting the pulse width to the memory pulse width,
When the waveform of (b) was applied, a high contrast of 15 to 30 was obtained. In this case, a good black state can be maintained even when bias is applied, and it can be concluded that the fluctuation of molecules due to bias voltage is suppressed.

Furthermore, as is clear from FIGS. 9 to 11,
The tilt angle θ of the liquid crystal is 16° or less, which is not so large compared to the pretilt angle. The smallness of this tilt angle is C
We believe that this is one of the reasons why the 1U orientation appears, and in that orientation, good bistable switching can be achieved and high contrast can be obtained.

Comparative Example 1 Ferroelectric liquid crystal element No. 1 was prepared in the same manner as in Example 3, except that the alignment film PSI-X-A-2001 used in Example 3 was replaced with another alignment film shown in Table 4. 301-305 were produced. Table 5 summarizes the combinations of alignment films and liquid crystals tested. 1 shown in FIG. 8(b) in the same manner as in Example 3.
/3 A bias waveform voltage (V = ±20V) was applied, the memory pulse width was measured, the pulse width was set to the memory pulse width, and the waveform shown in Figure 8(b) was applied, but 2 ~
Only a low contrast of about 7 was obtained.

[0065]

[Table 5]

Comparative Example 2 Ferroelectric liquid crystal composition No. 2 used in Example 3 201-2
A ferroelectric liquid crystal element was produced in the same manner as in Example 3, except that 03 was replaced with the ferroelectric liquid crystal composition shown in Table 6. The orientation state was observed and the state of switching was observed by applying a voltage with the waveform shown in FIG. 8, but none showed CIU orientation and bistable switching at room temperature. Also,
The voltage of the 1/3 bias waveform (V
= ±20 V) was applied, the memory pulse width was measured, the pulse width was set to the memory pulse width, and the waveform shown in FIG. 8(b) was applied, but only a low contrast of 7 or less was obtained. The main points of the observation results are summarized in Table 7.

[0067]

[Table 6]

[0068]

[Table 7]

[0069]

According to the present invention, an alignment film in which the pretilt angle of the liquid crystal at the interface between the liquid crystal and the alignment film is 8° or more is used, the alignment film is subjected to a rubbing treatment, and a ferroelectric liquid crystal with the general formula Using a ferroelectric liquid crystal composition containing 95% by weight or more of the compound represented by (I) and having a tilt angle not larger than the pretilt angle of the liquid crystal at the interface between the liquid crystal and the alignment film by 5° or more, C1
By driving the ferroelectric liquid crystal element by a partial rewriting method using a 1/3 bias driving method in a temperature range where the U orientation appears, a ferroelectric liquid crystal element with large capacity and high contrast can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining a 1/3 bias driving method.

FIG. 2 is a schematic diagram for explaining a matrix type liquid crystal element.

FIG. 3 is a cross-sectional view of a ferroelectric liquid crystal device of the present invention.

FIG. 4 is a diagram for explaining the chevron layer structure and zigzag defects of the chiral smectic C phase.

FIG. 5 is a diagram for explaining the orientation state of molecules in a chiral smectic C phase.

FIG. 6 is a diagram for explaining the relationship between rubbing alignment treatment and pretilt of liquid crystal molecules.

FIG. 7 is a diagram for explaining switching of ferroelectric liquid crystal.

FIG. 8 is a diagram showing applied voltage waveforms.

FIG. 9 is a diagram showing temperature changes in memory angle, tilt angle, and memory pulse width of a ferroelectric liquid crystal element according to an example of the present invention.

FIG. 10 is a diagram showing temperature changes in memory angle, tilt angle, and memory pulse width of a ferroelectric liquid crystal element according to an example of the present invention.

FIG. 11 is a diagram showing temperature changes in memory angle, tilt angle, and memory pulse width of a ferroelectric liquid crystal element according to an example of the present invention.

[Explanation of symbols]

1a, 1b glass substrate 2a, 2b
Transparent electrodes 3a, 3b Electrode protective film 4
a, 4b Orientation film 6 Seal member 7
LCD 9, 10 board
11 Liquid crystal cell 12a, 12b Polarizing plate 13 Smectic layer 15
Lightning defect 16 Hairpin defect 17, 18 Chevron structure 19 Rubbing direction 20 Liquid crystal molecule: N Director 21
C director 22 Pretilt angle 23 C1 orientation 24 C2 orientation 25 Normal line of smectic layer 26 Tilt angle of liquid crystal 27 Roller

Claims (6)

[Claims] 1. Electrodes are selectively formed on the surfaces of a pair of insulating substrates, an insulating film and an alignment film are formed, and the alignment film is subjected to a rubbing alignment treatment, and then the pair of substrates is , a ferroelectric liquid crystal is interposed between the substrates, and driving means for switching the optical axis of the liquid crystal by selectively applying a voltage to the electrodes and optical axis identification are provided. In the ferroelectric liquid crystal element, the directions of the rubbing alignment treatment of the pair of substrates are parallel, the pretilt angle of the liquid crystal molecules at the interface with the alignment film is 8° or more, and the liquid crystal to be driven is The phase is a chiral smectic C phase, and the chiral smectic C
In the phase, the smectic layer structure has a chevron structure bent in a dogleg shape, and in the driving temperature range, the direction of the rubbing alignment treatment and the direction of layer bending are opposite, and the ferroelectric liquid crystal The orientation state of is uniform, and the ferroelectric liquid crystal has a general formula (I
) A ferroelectric liquid crystal device comprising 95% by weight or more of a compound represented by the following formula: 2. The compound of general formula (I) has sub-formula (II
) [Chemical formula 2] or sub-formula (IV) [Chemical formula 4] At least one compound represented by sub-formula (III) [
Claim 1 consisting of at least one compound represented by:
The ferroelectric liquid crystal element described above. 3. The compound of general formula (I) has sub-formula (V)
The ferroelectric liquid crystal device according to claim 1 or 2, comprising at least one compound represented by the following formula. 4. The compound of general formula (I) has sub-formula (VI
) [Claim 6]
3. The ferroelectric liquid crystal element according to 3. 5. The tilt angle of the ferroelectric liquid crystal is not larger than the pretilt angle of the liquid crystal at the interface between the liquid crystal and the alignment film by 5° or more in the driving temperature range.
The ferroelectric liquid crystal element described in . 6. A ferroelectric liquid crystal containing 95% by weight or more of the compound of general formula (I) according to claim 1 is provided between a plurality of scanning electrodes and a plurality of signal electrodes arranged in directions crossing each other. A ferroelectric liquid crystal at the intersection of the scanning electrode and the signal electrode is used as a pixel, and a signal voltage with a waveform corresponding to display data is applied to the signal electrode, and the display state of the pixel on the scanning electrode is applied to the scanning electrode. When the display state of the pixel is not rewritten for the voltage applied to the ferroelectric liquid crystal when the display state of the pixel is rewritten when driving by applying a selection voltage with a waveform that can rewrite the pixel display state line-sequentially. 1. A method of driving a ferroelectric liquid crystal element, comprising using a driving waveform such that the voltage applied to the ferroelectric liquid crystal is 1/3 of the voltage.